The present invention is with respect to a process for compacting foundry mold-making material, that is filled into a closed mold space loosely over a pattern, using a compressed gas acting on the surface of the mold-making material and which undergoes expansion out of a high-pressure inlet space through an opening, that is able to be shut, into and in the mold space.
For compacting foundry mold-making materials a number of different methods, that are of a mechanical, pneumatic or of a mixed mechanical-pneumatic nature, have been put forward in the prior art. The present invention is however limited to pneumatic processes. Such processes may be put into two groups, that is to say a first group in which mold material is put under pressure in an inlet space and, on opening a valve, is blown or blasted together with the air into the mold space. In this process however a later mechanical pressing operation on the mold material is necessary each time in the flask using a high pressing force, the German Auslegeschrift specification No. 2,844,464 for example being representative of such a method. In the other group the mold material is loosely heaped onto the pattern and then acted upon by compressed air from the back of the mold. Examples of such a method are to be seen in the German Auslegeschrift specifications Nos. 2,844,464 and 1,961,234.
This second group or family of methods, may for its part be thought of as two different lines of development. In the one line (see the said German specification No. 2,844,464) compressed air from the plant air line is blown at a pressure of up to 7 bar for between 0.2 and 1 second one or more times through openings in a hollow end plate of the mold space with the purpose of causing the air to make its way out again through openings in the pattern plate after flowing through the foundry sand. In this case as well later ones, mechanical pressing is necessary for compacting the back of the mold on the one hand and on the other hand for clearing any air that is still present in the mold material and which was taken up therein because of the fluidizing effect. This mechanical pressing is supported by the use of vacuum as well. The plant is not made simpler to any marked degree than plants based on the use of blasting or blowing operations.
In the other line of this family or prior art process developments, see German specification No. 1,961,234, operation takes place in a high pressure range, that is to say, the pressure in the inlet space is very much greater than the line pressure in a foundry of up to 7 bar. In this known process the inlet pressure to be used is in fact between 20 and 100 bar, and the air at this pressure undergoes expansion within a time of at the most 0.15 second, so that it is then possible to do without the otherwise necessary further pressing step. A further condition necessary for running the process with the desired effect is that of having a certain ratio between the gas throughput rate on the one hand and the amount of the mold making material on the other, that is to say so as to have a ratio of between 5:1 and 40:1, such ratio furthermore being controlling for and giving a relation between the gas flow rate and the size of the mold flask. The said German specification No. 1,961,234 furthermore has a mold making machine in which there is a pressure vessel forming the inlet space or anti-chamber over the closed flask or over a filling frame that is put on top of it. There is a mechanically worked valve for joining the inlet space with the mold space. For the purpose of obtaining a reasonable overall size of apparatus using mold flasks of the standard size, a feed pressure of 100 bar was to be used in order to get the desired degree of compaction after expansion into the mold space. However such high pressure is likely to be the cause of an uneven surface of the molding material when the compressed gas violently takes effect on the back of the mold and the plant is made very much more complex in view of the need for producing such high pressures and making the structure walling in the mold space pressure-resistant enough. It would seem to be in view of this fact that there has been the further suggestion in the prior art of causing a distribution of the compressed gas evenly over the back of the mold before acting on the back of the mold, the gas furthermore having to be let off through a large number of openings in the pattern plate. These openings are however again likely to be the cause of trouble conditions inasfar as they become stopped up with mold making material.